extmark: fix decoration ploblems with extmark

54ce101 changed the way undo entries are created when adding decorations.
This creates all sorts of problems.This change fixes the problem by
reverting to the previous behavior.

src/nvim/api/buffer.c

@@ -1534,7 +1534,7 @@ Integer nvim_buf_add_highlight(Buffer buffer,
   ns_id = extmark_set(buf, ns_id, 0,
                       (int)line, (colnr_T)col_start,
                       end_line, (colnr_T)col_end,
-                      decoration_hl(hl_id), kExtmarkUndo);
+                      decoration_hl(hl_id), kExtmarkNoUndo);
   return src_id;
 }
 
@@ -1664,7 +1664,7 @@ Integer nvim_buf_set_virtual_text(Buffer buffer,
   Decoration *decor = xcalloc(1, sizeof(*decor));
   decor->virt_text = virt_text;
 
-  extmark_set(buf, ns_id, 0, (int)line, 0, -1, -1, decor, kExtmarkUndo);
+  extmark_set(buf, ns_id, 0, (int)line, 0, -1, -1, decor, kExtmarkNoUndo);
   return src_id;
 }
 

src/nvim/extmark.c

@@ -783,7 +783,7 @@ void bufhl_add_hl_pos_offset(buf_T *buf,
     }
     (void)extmark_set(buf, (uint64_t)src_id, 0,
                       (int)lnum-1, hl_start, (int)lnum-1+end_off, hl_end,
-                      decor, kExtmarkUndo);
+                      decor, kExtmarkNoUndo);
   }
 }
 

test/functional/api/highlight_spec.lua

@@ -7,6 +7,7 @@ local meths = helpers.meths
 local funcs = helpers.funcs
 local pcall_err = helpers.pcall_err
 local ok = helpers.ok
+local assert_alive = helpers.assert_alive
 
 describe('API: highlight',function()
   local expected_rgb = {
@@ -145,4 +146,15 @@ describe('API: highlight',function()
     eq({foreground=tonumber("0x888888"), background=tonumber("0x888888")},
        meths.get_hl_by_name("Shrubbery", true))
   end)
+
+  it("nvim_buf_add_highlight to other buffer doesn't crash if undo is disabled #12873", function()
+    command('vsplit file')
+    local err, _ = pcall(meths.buf_set_option, 1, 'undofile', false)
+    eq(true, err)
+    err, _ = pcall(meths.buf_set_option, 1, 'undolevels', -1)
+    eq(true, err)
+    err, _ = pcall(meths.buf_add_highlight, 1, -1, 'Question', 0, 0, -1)
+    eq(true, err)
+    assert_alive()
+  end)
 end)

test/functional/ui/inccommand_spec.lua

@@ -2750,6 +2750,26 @@ it(':substitute with inccommand, timer-induced :redraw #9777', function()
   ]])
 end)
 
+it(":substitute doesn't crash with inccommand, if undo is empty #12932", function()
+  local screen = Screen.new(10,5)
+  clear()
+  command('set undolevels=-1')
+  common_setup(screen, 'split', 'test')
+  feed(':%s/test')
+  sleep(100)
+  feed('/')
+  sleep(100)
+  feed('f')
+  screen:expect([[
+  {12:f}           |
+  {15:~           }|
+  {15:~           }|
+  {15:~           }|
+  :%s/test/f^  |
+  ]])
+  assert_alive()
+end)
+
 it('long :%s/ with inccommand does not collapse cmdline', function()
   local screen = Screen.new(10,5)
   clear()